India ranked fourth in the list of countries sending out spam e-mails with malicious content like ads for pharma products and sexually explicit material, a Microsoft report has said.

The US topped the list of countries having sent maximum number of botnet spam during January-June 2013, followed by China, the UK and India, the survey said.

Cyber criminals distribute malicious software or malware that can turn a computer into a bot, also known as a zombie or robot, which makes the computer perform automated tasks over the Internet, without the PC owner's knowledge.

"The countries and regions sending the most spam from botnets in H1 13 were the US (29,216 IP addresses sending spam), China (16,094), the UK (7,728) and India (5,779)," Microsoft said in its Security Intelligence Report.

Determining the originating place of botnet spam can help governments and industry response teams better understand the magnitude of security problems affecting different areas of the globe, it added.

India was also victim of a number of cybercrimes, ranking fifth in terms of malware encounters during January-June 2013.

"In India, the encounter rate increased slightly from 29.31 per cent in Q1 2013 to 29.44 per cent in Q2 2013. Autorun (encountered by 7.6 per cent of computers in India in 2Q13), Gamarue (4.7 per cent) and the virus family Win32/Sality (4.4 per cent) were among the most commonly encountered threats," it said.

Encounter rate refers to a percentage of computers running Microsoft real-time security products encountering malware during the said period.

The US topped this list too, followed by Brazil, Russia and Turkey. Other countries in the list included Mexico, Germany, France, China and the UK.

Worms were most prevalent form of attack in India, followed by trojans and viruses.

Microsoft, in a separate study last year, had said computer users will have to spend 1.5 billion hours and USD 22 billion identifying, repairing and recovering from the impact of malware.

Global enterprises are also estimated to have spend USD 114 billion to deal with the impact of malware-induced cyber attacks, it had said.